Title

Author

Date of Award

8-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Microbiology

Advisor

Campbell, Barbara J

Committee Member

Henson, J. Michael

Committee Member

Kurtz, Jr., Harry D

Abstract

Microbes are important contributors to ecosystem processes such as biogeochemical cycling. Their activities vary, depending on environmental parameters such as carbon type and concentration, temperature, and salinity. Current estimates of in situ microbial growth is limited to gross estimates or rely on incubation based methods that disturb the natural state of the community. The goal of this masterâ€™s thesis is to develop molecular methods to directly assess microbial growth rates in the environment at the level of a taxonomic group. Here we grew Ruegeria pomeroyi DSS-3 under different temperatures (15 Â°C or 30 Â°C) and different carbon sources (yeast extract/tryptone, glucose, or acetate). We then characterized differences in growth rates and gene expression either with select growth-related genes (rpoD, rpoB, rpoS, rplB, and ftsI) or of the whole transcriptome. Ratios of rpoB and rplB mRNA:mRNA genes were significantly upregulated in log versus stationary phase as measured by qPCR for all three experiments utilizing a minimal media. Acetate-grown cells exhibited significant differences between growth phases for all five genes. These results indicate expression of the selected genes depend on growth phase as well carbon source availability. Conversely, a negative correlation between growth-related mRNA per cell and specific growth rate was observed. We also examined changes in other genes in log vs. stationary phases of growth using a transcriptomics approach. The bulk of differentially expressed genes were involved in amino acid transport and metabolism as well as translation and ribosomal structure. Our cultivation-based results indicate that monitoring differences in specific growth-related transcripts levels is a viable option for determining growth-related activity changes in microbial taxa in marine environments. Future experiments should include growth in a mixed culture and with other bacteria with different ecological strategies in order to generalize our results to the total marine microbial community.